1. Field of the Invention
This invention relates generally to oil field equipment, and more particularly to an improved drawworks.
2. Description of the Related Art
A drawworks, sometimes referred to as a hoist, is a large piece of oil field equipment which can broadly be described as a very large winch. The drawworks is mounted on an oil or gas well drilling rig, its sole function being to raise and lower drill pipe and casing into and out of the bore hole. Typically, a drawworks is provided with: a hollow drum which is coaxially mounted on a drum shaft; a source of power to cause the drum shaft and drum to rotate; some means of transmitting power from the power source to the drum shaft; and, some means of braking the drum. The drawworks is mounted on the drilling rig such that the longitudinal center axis of the drum and drum shaft is coplanar with the drilling rig platform, or horizontal. Examples of the power source are AC motors, DC motors, and diesel or other types of engines. The power is generally transmitted from the power source to the drum shaft either by (1) a chain transmission mechanism or (2) a gear transmission mechanism. The drum can be braked in a number of ways, examples of which are by disc brakes, band brakes, water-cooled brakes, electric brakes, or by the power source. The drum is wrapped with a length of wireline, normally not provided with the drawworks. The wireline is fed upwardly from the drawworks to the top of the oil derrick and then downwardly such that it can be attached to the drill pipe or casing. Between the top and bottom of the derrick, the wireline is passed through a series of sheaves (or pulleys), which are housed within a crown block and traveling block. The lowermost end of the wireline is attached to a hook and swivel arrangement, to which the drill pipe and casing may be releasably attached, and thereby raised and lowered.
Problems can arise with conventional drawworks of the type described above. One very serious problem, which the present invention is believed to solve, arises in the event that one of the components of the drawworks fails. The most common failures are mechanical in nature, and occur either in the power source (motor or engine) or in the gear or chain mechanism. In the event that such a mechanical failure occurs, the drawworks will become completely disabled, and thus unable to perform its function. If the failure can be quickly remedied, and the drawworks quickly restored to operation, then no problems should arise. However, in the event that the failure is of such a serious nature that it cannot be quickly remedied, such that the entire drilling operation must be halted for a period of time, then it is almost inevitable that the drill pipe will become "stuck" in the bore hole. The drill pipe becomes "stuck" because, after sitting in the same position for an extended period of time, rock, dirt and other debris tends to cave in around the pipe and on top of the drilling bit, which is attached to the lowermost end of the drill pipe. Those skilled in the oil well drilling industry know that a "stuck" drill pipe can be disastrous and extremely expensive to remedy, and could potentially lead to the bore hole being completely abandoned. The drawworks of the present invention was developed to reduce the risk of the drill pipe becoming "stuck." As will be more fully described below, the drawworks of the present invention is provided with complete redundancy, which means that if a mechanical failure occurs, the drawworks will still have the ability to raise the drill pipe out of the well hole, or at least up into the casing, before the drill pipe becomes "stuck."